1. Field of the Invention
The present invention relates to a silver halide photographic emulsion, a method of preparing the same, and a light-sensitive material containing this emulsion.
More specifically, the present invention relates to a silver halide photographic emulsion having a low fog and an improved sensitivity and a resistance to pressure, a method of preparing the same, and a light-sensitive material containing this emulsion.
2. Description of the Related Art
Recently, a demand for photographic silver halide emulsions has been increasingly strict, and higher level demands have arisen for toughness, such as a resistance to pressure, in addition to photographic properties, such as a high sensitivity and a good graininess.
It is considered preferable in terms of uniformity of chemical sensitization that silver iodide (iodide ion) contents be uniform between individual silver halide grains in order to increase the sensitivity and improve a resistance to pressure of the grains.
Conventionally, the following iodide ion supply methods have been available as a method of forming a silver halide phase containing silver iodide in the process of forming silver halide grains.
That is, the methods are a method of using an aqueous iodide salt solution, such as an aqueous KI solution, and a method of using fine silver halide grains containing silver iodide or using an iodide ion-releasing agent, disclosed in JP-A-2-68538 (Japanese Patent Application No. 63-220187; "JP-A" means Published Unexamined Japanese Patent Application).
In the method of using an aqueous iodide salt solution, however, grain growth is performed in a region where the nonuniformity of the concentration distribution of iodide ions is large due to the addition of free iodide ions to a reaction solution. Therefore, it is impossible to perform uniform grain growth between individual grains.
The technique disclosed in the above patent application, on the other hand, performs grain growth in which a halogen composition (a microscopic distribution of silver iodide) is uniform inside each grain and between individual grains.
In the method of using fine silver halide grains containing silver iodide, however, the dissolution of the fine grains is too slow to rapidly generate iodide ions.
Also, the above patent application has no description concerning a technique of generating iodide ions rapidly during grain growth, which is applicable to the method using an iodide ion-releasing agent.
That is, the above patent application performs formation of silver halide grains such that no microscopic nonuniformity in silver iodide is produced, i.e., silver iodide is uniformly contained throughout the entire process of forming a silver halide phase containing silver iodide. Therefore, silver halide grains formed through the use of the technique of that patent application are still unsatisfactory to meet the above requirements, i.e., a sufficient decrease in fog, a high sensitivity, and an improvement in a resistance to pressure.